fall crocus

Russell in Michigan wrote,
>All appear to be reliably winter-hardy here. I know of a plantsman in
>Wisconsin who winters C. goulimyi.
That's hard to understand when the ground freezes so deeply in the upper
Midwest, and these crocuses start growth in fall. Does the ground never
thaw during the winter? Are they somehow in suspended animation? How can
they survive?
In milder, but still cold-winter, climates, repeated freezing and thawing
are hard on low-elevation Mediterranean crocuses.
Jane McGary
Northwestern Oregon, USA